如何在WebGL中将不同的纹理映射到多维数据集的不同面？

Question

我有以下立方体坐标：

{
   "ServerUnavailable":"true",
   "IssueType":"Maintenance",
   "ErrorMessage":"Servers are currently down for maintanance, please try again later"
}

这些是纹理坐标：

var vertices = [
    // Front face
    -1.0, -1.0,  1.0,
     1.0, -1.0,  1.0,
     1.0,  1.0,  1.0,
    -1.0,  1.0,  1.0,

    // Back face
    -1.0, -1.0, -1.0,
    -1.0,  1.0, -1.0,
     1.0,  1.0, -1.0,
     1.0, -1.0, -1.0,

    // Top face
    -1.0,  1.0, -1.0,
    -1.0,  1.0,  1.0,
     1.0,  1.0,  1.0,
     1.0,  1.0, -1.0,

    // Bottom face
    -1.0, -1.0, -1.0,
     1.0, -1.0, -1.0,
     1.0, -1.0,  1.0,
    -1.0, -1.0,  1.0,

    // Right face
     1.0, -1.0, -1.0,
     1.0,  1.0, -1.0,
     1.0,  1.0,  1.0,
     1.0, -1.0,  1.0,

    // Left face
    -1.0, -1.0, -1.0,
    -1.0, -1.0,  1.0,
    -1.0,  1.0,  1.0,
    -1.0,  1.0, -1.0
];

现在，通过下面的代码，它只加载一个纹理图像。

var textureCoordinates = [
    // Front
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Back
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Top
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Bottom
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Right
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0,

    // Left
    0.0,  0.0,
    1.0,  0.0,
    1.0,  1.0,
    0.0,  1.0
];

我从MDN web docs得到了这个代码示例，我想知道我应该做什么修改，以便每个立方体面可以设置不同的纹理。我已经阅读了有关更改活动纹理的内容，但我不知道如何操作它以免影响整个多维数据集。我是WebGL的新手，我希望有人能帮助我理解这一点。

Answer 1

将不同图像放在立方体上的最佳方法是将所有图像放入一个纹理中，然后使用UV坐标为立方体的每个面选择纹理的不同部分。

See example on this page with lots of explanation

或者

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1],
  texcoord: [
 // select the bottom left image
    0   , 0  ,
    0   , 0.5,
    0.25, 0.5,
    0.25, 0  ,
    // select the bottom middle image
    0.25, 0  ,
    0.5 , 0  ,
    0.5 , 0.5,
    0.25, 0.5,
    // select to bottom right image
    0.5 , 0  ,
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 0  ,
    // select the top left image
    0   , 0.5,
    0.25, 0.5,
    0.25, 1  ,
    0   , 1  ,
    // select the top middle image
    0.25, 0.5,
    0.25, 1  ,
    0.5 , 1  ,
    0.5 , 0.5,
    // select the top right image
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 1  ,  
    0.5 , 1  ,
  ],
  indices:  [0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7, 8, 9, 10, 8, 10, 11, 12, 13, 14, 12, 14, 15, 16, 17, 18, 16, 18, 19, 20, 21, 22, 20, 22, 23],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

// calls gl.createTexture, gl.bindTexture, gl.texImage2D, gl.texParameteri
var tex = twgl.createTexture(gl, {
  src: "https://webglfundamentals.org/webgl/resources/noodles.jpg",
  crossOrigin: "",
});

var uniforms = {
  u_texture: tex,
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);
  var world = m4.rotationY(time);

  uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
  twgl.setUniforms(programInfo, uniforms);
  // calls gl.drawArray or gl.drawElements
  twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>

有很多理由说明它可以说是最好的方式。作为一个简单的例子，如果你实际制作了一个使用6个纹理的着色器，你需要一个不同的金字塔着色器（3-4个面），另一个用于二十面体（12个面），另一个用于十二面体（20面），如果你将图像放在一个纹理中，它就可以使用相同的着色器。

即使您想分别加载6个图像，最好制作2d画布，使用drawImage将所有6个图像复制到该画布中，然后将该画布复制到单个纹理中。

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [1, 1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, 1, 1, 1, 1, 1, 1, 1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, -1, 1, 1, 1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, 1, 1, -1, 1, -1, -1, -1, -1, -1],
  texcoord: [
 // select the bottom left image
    0   , 0  ,
    0   , 0.5,
    0.25, 0.5,
    0.25, 0  ,
    // select the bottom middle image
    0.25, 0  ,
    0.5 , 0  ,
    0.5 , 0.5,
    0.25, 0.5,
    // select to bottom right image
    0.5 , 0  ,
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 0  ,
    // select the top left image
    0   , 0.5,
    0.25, 0.5,
    0.25, 1  ,
    0   , 1  ,
    // select the top middle image
    0.25, 0.5,
    0.25, 1  ,
    0.5 , 1  ,
    0.5 , 0.5,
    // select the top right image
    0.5 , 0.5,
    0.75, 0.5,
    0.75, 1  ,  
    0.5 , 1  ,
  ],
  indices:  [0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7, 8, 9, 10, 8, 10, 11, 12, 13, 14, 12, 14, 15, 16, 17, 18, 16, 18, 19, 20, 21, 22, 20, 22, 23],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);


var ctx = document.createElement("canvas").getContext("2d");
ctx.canvas.width = 512;
ctx.canvas.height = 256;
ctx.fillRect(0, 0, 512, 256);  // black to start

var tex = gl.createTexture();
uploadCanvasToTexture();

[
  "https://i.imgur.com/weklTat.gif",
  "https://i.imgur.com/6AvnLa3.jpg",
  "https://i.imgur.com/HkzeCU2.jpg",
  "https://i.imgur.com/D9HVm6n.png",
  "https://i.imgur.com/7MlmkJr.jpg",
  "https://i.imgur.com/v38pV.jpg",
].forEach(function(url, ndx) {
  var img = new Image();
  img.onload = function() {
    addFaceToCanvasAndUploadToTexture(img, ndx);
  };
  img.crossOrigin = "";
  img.src = url;
});
  
function addFaceToCanvasAndUploadToTexture(img, ndx) {
  var x = ndx % 3;
  var y = ndx / 3 | 0;
  ctx.drawImage(img, 0, 0, img.width, img.height, x * 128, y * 128, 128, 128);
  uploadCanvasToTexture();
}
  
function uploadCanvasToTexture() {
  gl.bindTexture(gl.TEXTURE_2D, tex);
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, ctx.canvas);
  gl.generateMipmap(gl.TEXTURE_2D);
}    
    
var uniforms = {
  u_texture: tex,
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);
  var world = m4.rotationY(time);

  uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
  twgl.setUniforms(programInfo, uniforms);
  // calls gl.drawArray or gl.drawElements
  twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>

如果你真的需要每张脸的分辨率，那么第二种最常见的方法是制作6个平面并将它们定位，使它们形成一个立方体。在每个平面上放置一个纹理。绘制6个绘制调用，每个平面一个。

"use strict";
var m4 = twgl.m4;
var gl = document.getElementById("c").getContext("webgl");
// compiles shader, links and looks up locations
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [
    -1, -1, 0,
     1, -1, 0,
    -1,  1, 0,
     1,  1, 0,
  ],
  texcoord: [
    0, 0,
    1, 0,
    0, 1,
    1, 1,
  ],
  indices:  [
    0, 1, 2, 2, 1, 3,
  ],
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each array
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);
    
// calls gl.createTexture, gl.bindTexture, gl.texImage2D, gl.texParameteri
var textures = twgl.createTextures(gl, {
  face0: { src:"https://i.imgur.com/weklTat.gif", crossOrigin: "", },
  face1: { src:"https://i.imgur.com/6AvnLa3.jpg", crossOrigin: "", },
  face2: { src:"https://i.imgur.com/HkzeCU2.jpg", crossOrigin: "", },
  face3: { src:"https://i.imgur.com/D9HVm6n.png", crossOrigin: "", },
  face4: { src:"https://i.imgur.com/7MlmkJr.jpg", crossOrigin: "", },
  face5: { src:"https://i.imgur.com/v38pV.jpg", crossOrigin: "", },
});
    
var models = [
  { tex: textures.face0, local: m4.translate(m4.rotationY(Math.PI * 0.0), [0, 0, 1]), },
  { tex: textures.face1, local: m4.translate(m4.rotationY(Math.PI * 0.5), [0, 0, 1]), }, 
  { tex: textures.face2, local: m4.translate(m4.rotationY(Math.PI * 1.0), [0, 0, 1]), }, 
  { tex: textures.face3, local: m4.translate(m4.rotationY(Math.PI * 1.5), [0, 0, 1]), }, 
  { tex: textures.face4, local: m4.translate(m4.rotationX(Math.PI * 0.5), [0, 0, 1]), }, 
  { tex: textures.face5, local: m4.translate(m4.rotationX(Math.PI * 1.5), [0, 0, 1]), }, 
];

var uniforms = {
};

function render(time) {
  time *= 0.001;
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  gl.enable(gl.DEPTH_TEST);
  gl.enable(gl.CULL_FACE);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

  var projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 10);
  var eye = [1, 4, -6];
  var target = [0, 0, 0];
  var up = [0, 1, 0];

  var camera = m4.lookAt(eye, target, up);
  var view = m4.inverse(camera);
  var viewProjection = m4.multiply(view, projection);

  gl.useProgram(programInfo.program);
  // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  
  models.forEach(function(model) {
    var world = m4.rotationY(time);
    m4.multiply(model.local, world, world);
    uniforms.u_texture = model.tex;
    uniforms.u_worldViewProjection = m4.multiply(world, viewProjection);

    // calls gl.uniformXXX, gl.activeTexture, gl.bindTexture
    twgl.setUniforms(programInfo, uniforms);
    // calls gl.drawArray or gl.drawElements
    twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);
  });

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body { margin: 0px; }
canvas { width: 100vw; height: 100vh; display: block; }

<script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;

attribute vec4 position;
attribute vec2 texcoord;

varying vec2 v_texCoord;

void main() {
  v_texCoord = texcoord;
  gl_Position = u_worldViewProjection * position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec2 v_texCoord;

uniform sampler2D u_texture;
void main() {
  gl_FragColor = texture2D(u_texture, v_texCoord);
}
  </script>
<script src="https://twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>